Ignition Switch Signal Invalid
The U300C code indicates that a control module (typically the BCM, PCM, or gateway) has detected an invalid or implausible voltage signal on one or more ignition switch input circuits (Off, Accessory, Run, Start). This means the module cannot correctly determine the key position or start button state, preventing proper management of power and starting systems.
1. Commonly Affected Makes
This is a generic OBD2 code, potentially applicable to any manufacturer using this diagnostic standard.
2. Most Common Causes
- Faulty ignition switch (key or START/STOP button)
- Open, short-to-ground, or short-to-power in the ignition power supply circuits (Run/Start)
- Blown fuses or fusible links in the under-hood or interior fuse box
- Body Control Module (BCM) or Powertrain Control Module (PCM) internal failure
- Low battery voltage or loose/corroded battery connections
3. Symptoms You Will Notice
- Engine may not start or stalls unexpectedly
- Electrical accessories (radio, windows, etc.) may not work properly
4. Step-by-Step Diagnosis
Check battery voltage and clean/tighten battery terminals
Inspect ignition switch and related wiring for damage or corrosion
Test fuses and fusible links related to ignition circuits
Scan for additional codes and check module communication
Perform voltage drop tests on ignition switch circuits
5. Frequently Asked Questions
Is it safe to drive?▼
No, this code indicates a high-severity issue that can cause the engine to stall or fail to start, posing a safety risk. Have the vehicle diagnosed and repaired immediately.
How much does it cost to fix?▼
Repair costs typically range from $100 to $500, depending on whether the ignition switch, wiring, or a control module needs replacement.